In recent years, a calcineurin inhibitor such as cyclosporine and FK506 is used to decrease rejections in patients who received organ transplants. However, a certain kind of calcineurin inhibitor such as cyclosporine sometimes causes toxic side effects such as nephrotoxicity, hepatotoxicity, neurotoxicity and the like. Thus, the development of a safer and highly effective medicament is ongoing to decrease rejections in patients after transplantation.
Patent documents 1-3 disclose 2-aminopropane-1,3-diol compounds useful as an (acute or chronic) rejection suppressant in organ or bone marrow transplantation, or as a therapeutic drug for various autoimmune diseases such as psoriasis, Behcet's disease and the like, or rheumatological diseases.
One of these compounds, 2-amino-2-[2-(4-octylphenyl)ethyl]propane-1,3-diol hydrochloride (hereinafter sometimes to be referred to as FTY720) is a compound currently under clinical development as a rejection suppressant in kidney transplantation or a therapeutic drug for multiple sclerosis. FTY720 is rapidly converted to phosphorylated FTY720 [hereinafter sometimes to be referred to as FTY720-P, for example, 2-amino-2-phosphoryloxymethyl-4-(4-octylphenyl)butanol] by sphingosine kinase in the body. FTY720-P acts as an agonist on 4 kinds of SIP receptors (except S1P2) out of 5 kinds of sphingosine-1-phosphate (hereinafter sometimes to be referred to as S1P) receptors (hereinafter sometimes to be referred to as S1P1-S1P5) (non-patent document 1).
It has been recently reported that S1P1 in the SlP receptors is essential for emigration of mature lymphocytes from the thymus and secondary lymphoid tissues. FTY720-P down-regulates S1P1 on lymphocytes by acting as an S1P1 agonist. As a result, it has been suggested, the emigration of mature lymphocytes from the thymus and secondary lymphoid tissues is inhibited, and circulating mature lymphocytes in the blood are isolated in the secondary lymphoid tissues, whereby an immunosuppressive action is exhibited (non-patent document 2).
On the other hand, conventional 2-aminopropane-1,3-diol compounds are feared to cause transient bradycardia expression as a side effect, and to solve this problem, many novel compounds obtained by modifying the chemical structure of 2-aminopropane-1,3-diol compound have been reported. From such compounds, as a compound with a substituent added to a benzene ring of FTY720, patent document 4 discloses an aminopropanol derivative as an SlP receptor modulator having a phosphate group, and patent documents 5 and 6 both disclose aminopropanol derivatives as S1P receptor modulators. However, a trihaloalkyl group, for example, a trifluoromethyl group, is not disclosed as a substituent on the benzene ring in these documents. In any event, none of them have reached a satisfactory level as regards the safety of a pharmaceutical product, as the situation now stands.    patent document 1: WO 94/08943    patent document 2: WO 96/06068    patent document 3: WO 98/45249    patent document 4: WO 02/076995    patent document 5: WO 2004/096752    patent document 6: WO 2004/110979    non-patent document 1: Science, 2002, Vol. 296, pages 346-349    non-patent document 2: Nature, 2004, Vol. 427, pages 355-360